I've jumped into 100-120 mile rides without much training or preparation. The key things that I found:

- bring stuff to fix things. Flat tire, multi tool for loose things, etc. In a committed ride like yours (aka one way, not a loop or out and back) it's tough if you have to stop because of a fixable mechanical.
- eat and drink. After doing a few of these "not-much-training-before" long rides I found that I ride best if I eat/drink every 90 minutes or so. 60 minutes is too frequent, 2 hours is just a touch too long. You need to keep some sugars in your blood but also you need protein/fat. I'll eat various things - peanuts is one odd thing. Pop Tarts are good, as well as regular gels and bars. I prefer protein bars for long rides, like the Builder Bar, etc, because of the protein in them. That keeps you from feeling totally empty 5-6 hours in.
- your biggest issue will be cramps. You can ride through sore legs, sore butt, bonking, whatever, but you can't ride through if you have cramped up legs. I mean, okay, you can sort of recover, but it becomes a survival thing. The last long ride I did I started cramping 45 minutes into the ride yet I made it 4.5 hours while judiciously favoring various parts of my legs. The best defense against cramps is being super fit. The next best thing is to be hydrated and fueled.
- don't worry about your initial pace. If you have reserves you can finish strong. On my super long rides (over 5 hours) I usually averaged my fastest speed in the last hour - there were a bunch of factors, including failing daylight, dropping temperatures, and the lure of being back at home base.
- finally, start as early as you can. Don't think "Oh we'll have time to eat with the family first" or whatever. Get up, eat something quick, go to the bathroom, and go. You can always hang out after the ride but if it's 8 PM and the sun is setting and you're 20 miles from your goal and feeling good you'll be bummed. I've finished 100+ mile rides in pitch black (in sunglasses no less - prescription so I couldn't remove them and ride safely). I resorted to riding on sidewalks when cars showed up. If I'd left an hour or two earlier I'd have been fine. You'll be really happy if you leave at 7 AM and after doing about 90 miles at a not-too-bad pace you see that it's only noon or 1 PM. This gives you a lot of time to work through any issues, cramps or whatever.

To put my long rides in perspective in terms of pace I might average 16-17 mph solo on a moderately hard ride hour long ride on flat terrain. I'll do 13-15 mph on an easy hour long ride, same roads. In races I'll average 25-27 mph okay for an hour to 90 minutes (drafting, flat terrain, Cat 3s mainly). On my long rides I'll average 14-15 mph, and I've done as high as 21 mph for the last hour at the end of a 120 mile all-solo ride. My longest ride is about 125-130 miles so I have no experience beyond that distance.

In the last 10 years or so I've only done two long rides with other riders, one ride with one teammate/friend (106 miles), the other with about 7 others whom I'd never met before (125+ miles). Don't be afraid to sit in. You'll go through some up and down periods. Remember that taking longer pulls is more beneficial to your riding companion than pulling faster so if you're feeling spectacular pull a bit longer. If you don't then don't pull and if you're struggling on wheels then ask to ease up. Don't overdo it on the hills at the beginning. Those "easy" efforts to jump up little hills really takes the sap out of your legs later. It's only as you get into the 80-90 mile mark where you can start picking up your effort safely, at least for a 130 mile ride.

Good luck and let us know how it goes.